JPH03216598A - Device for decreasing discharge of radioactive substances - Google Patents

Abstract

PURPOSE:To prevent direct discharge of radioactivity from a building, caused by decrement of negative pressure inside the building, with using a normal ventilation system, by continuing operation of the normal ventilation system until a rated operational condition of an emergency gas treatment system is reached, in case of an accident. CONSTITUTION:In the device for decreasing discharge of radioactive substances in this invention, an accident signal 11 is blocked by a block circuit when the signal 11 is generated and therewith an exhaust isolation valve 9 is held at an opening condition even after the signal is generated, and also the exhaust fan 7 is continuously operated. With this procedure, decrement of negative pressure inside a building can be prevented and moreover, if required, control so as to enhance the negative pressure is also possible. Also, even in case that an electrical power source is lost, the exhaust fan 7 keeps running for a certain period and can hold the pressure inside the building to be negative, but, because of a time limit of its exhausting function, the blocking circuit is to be released after a certain time period elapses, and the exhaust isolation valve 9 is closed down in order to keep the negative pressure inside the building until commencement of a rated operation of the emergency gas treatment system.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention is directed toward discharging radioactive materials generated during a reactor accident at a nuclear power plant out of the reactor building M (hereinafter simply referred to as the building). This invention relates to radioactive material release reduction equipment that prevents the release of radioactive materials.

(Conventional technology) Nuclear power plant buildings are equipped with radioactive material release reduction equipment to prevent radioactive material leaking from the reactor containment vessel from dispersing outside the building in the event of a nuclear reactor accident. .

Figure 2 shows conventional radioactive material release reduction equipment.

In this diagram, the radioactive material release reduction equipment consists of a regular ventilation system that ventilates the inside of the building during normal operation, and an emergency gas treatment system that removes radioactive materials leaked into the building and exhausts the air inside the building in the event of an accident. It becomes more.

First, the regular ventilation system is as follows. In other words, building 1
Air is supplied from one side through an air supply duct 4 by two air supply fans 3 of an air supply device 2.

Two air supply isolation valves 5 are provided in the portion of the air supply duct 4 inside the building 1. Further, exhaust air is exhausted from the other side of the building 1 through an exhaust duct 8 by two exhaust fans 7 of an exhaust device 6. Two exhaust isolation valves 9 are provided in the portion of the exhaust duct 8 inside the building 1. Note that the discharge side of the exhaust fan 7 is communicated with the bottom of the exhaust pipe 10 having a predetermined height.

Therefore, the supply air fan 3 and the exhaust fan 7 of the above-mentioned regular ventilation system
The supply air isolation valve 5, exhaust isolation valve 9, etc. are stopped and closed when the accident signal 11 is issued.

On the other hand, the emergency gas treatment system is as follows. That is,
Two drying devices 14 each communicating with the atmosphere inside the building via an inlet valve 12 and a flow rate adjustment valve 13, and two blowers 1 sucking air inside the building through these drying devices.
5. Filter device 1 connected to the discharge port side of these blowers
6. Two outlet valves 17 are provided in parallel on the downstream side of this filter device, and the downstream side of the outlet valve 17 is connected to a duct opening at the upper end of the exhaust pipe 10. The inlet valve 12, flow rate adjustment valve 13, blower 15, and outlet valve 17 of the emergency gas treatment system are activated when the accident signal 11 is issued.

The conventional radioactive material emission reduction equipment configured as described above operates as follows. When the nuclear reactor is in normal operation, air is supplied and exhausted by the air supply device 2 and the exhaust device 6, and the air in the building 1 is maintained at a required level of cleanliness. Note that the air supply device 2 is equipped with a filter, and outside air is supplied into the building 1 after removing dust. Further, the exhaust device 6 is similarly equipped with a filter, and the air inside the building is discharged from the exhaust stack 10 above dust removal.

If any kind of accident occurs, accident signal 11 will be issued and the air supply system of the regular ventilation system will be alerted! The supply air fan 3 of No. 2 and the exhaust fan 7 of the exhaust device 6 are stopped, and the supply air isolation valve 5 and the exhaust isolation valve 9 are closed.

At the same time, the inlet valve 12, flow rate adjustment valve 13, and outlet valve 17 of the emergency gas treatment system are opened, and the blower 15 is started. Therefore, radioactive substances leaked from the reactor containment vessel and mixed into the atmosphere inside the building are removed by drying device 14 and filter 1.
6 etc., and clean air is exhausted from the exhaust pipe 10. Note that the inside of the building 1 is maintained at a slight negative pressure by suction and exhaust by the blower 15 in the above-mentioned regular ventilation system, and leakage of atmosphere from various parts of the building is prevented.

(Problem to be Solved by the Invention) However, in the conventional radioactive material release reduction equipment described above, when an accident signal is issued, the regular ventilation system is stopped and the emergency gas processing system is started, and the system has to wait until it reaches rated operation. There is a time lag.

Specifically, it takes 30 seconds to 1 minute for the emergency gas treatment system to reach its rated operation even when there is no power loss. In addition, in the event of a power loss accident, the emergency power supply equipment (diesel generator) must be started, so it takes an even longer time of 1 to 2 minutes to bring the emergency gas processing system to its rated operation. do.

Until the above emergency gas treatment system reaches its rated operation,
The temperature inside the building is increased by the heat from the heating element inside the building, and the air inside the building is thereby heated and the air expands. Additionally, outside air leaks into the building during the time lag depending on the leakage rate of the building. Expansion of the air inside the building mentioned above;
Any leakage of outside air into the building will result in a drop in negative pressure inside the building, and there is a risk that the air inside the building containing radioactive materials will be released to low places from leak points in the building.

The present invention has been made based on the above circumstances, and it maintains the necessary negative pressure inside the building until the emergency gas treatment system is activated and reaches rated operation in the event of an accident. The purpose is to provide radioactive material release reduction equipment that can prevent indoor air leakage at low locations.

[Configuration of the Invention (Means for Solving the Problems) The radioactive material release reduction equipment of the present invention includes a regular ventilation system equipped with a supply air fan, an exhaust fan, a supply air isolation valve, and an exhaust isolation valve, and a A system having an emergency gas treatment system that removes radioactive materials and exhausts the inside of the building, characterized in that, in the event of an accident, the operation of the regular ventilation system is continued until the rated operation of the emergency gas treatment system is reached. do.

(Function) In the radioactive material release reduction equipment of the present invention having the above configuration, even after an accident occurs, the exhaust isolation valve is kept open,
Continue operating the exhaust fan.

Thereby, it is possible to prevent the negative pressure in the building from decreasing until the emergency gas treatment system reaches its rated operation, and if necessary, it is also possible to control the negative pressure to be increased.

(Embodiment) FIG. 1, in which the same parts as in FIG. 2 are given the same reference numerals, shows an embodiment of the present invention. In this figure, a block circuit 18 is provided between the branches where the signal system accident signal 11 is supplied to the supply air isolation valve 5 and the exhaust air isolation valve 9 of the normal ventilation system, and this block circuit is connected to the outside air and the building air. A differential pressure setting device 19 is connected to the differential pressure setting device 19 for setting the differential pressure within. Furthermore, the radiation monitor 20 provided outside the exhaust duct 8 is also connected to the block circuit 18.
It is connected to the.

In the radioactive material release reduction equipment of the present invention having the above configuration,
The operation of the normal ventilation system during normal reactor operation is exactly the same as in the conventional system described with reference to FIG.

When a nuclear reactor accident occurs, an accident signal 11 is issued, which issues a stop command to the supply air fan 3 of the regular ventilation system and a close command to the supply air isolation valve 5. At the same time, the inlet valve 12, flow rate adjustment valve 13, and outlet valve 17 of the emergency gas treatment system are opened, and the blower 15 is started. However, the above-mentioned inlet valve 12, flow rate adjustment valve 13, outlet valve 1
It takes about 30 seconds for blower 7 to fully open, and about 30 seconds for blower 15 to reach its rated rotation, so it takes about 30 seconds for blower 15 to reach its rated rotation, so it takes about 30 seconds for blower 15 to reach its rated speed, so it takes about 30 seconds for blower 15 to reach its rated speed, so it takes about 30 seconds for blower 15 to reach its rated rotation, so it takes about 30 seconds for blower 15 to reach its rated speed. It takes at least 30 seconds after the release, and in some cases about 1 minute.

Therefore, when the regular ventilation system is in operation, several nnA g ~ 20W
The air pressure inside the building was controlled to a slight negative pressure of mAg.
If the normal ventilation system is stopped at the same time as the accident signal is issued,
There is no control at all during the delay time. During this time, the negative pressure inside the building decreases due to the leak-in of outside air from outside the building and the thermal expansion of the air inside the building due to the temperature rise due to heat from the heating element inside the building.

In the present invention, a block circuit 18 is provided, which blocks the accident signal 11, keeps the exhaust isolation valve 9 open even after the accident signal is issued, and keeps the exhaust fan 7 open.
continue to operate. Further, in this embodiment, the building negative pressure is detected by the differential pressure setting device 19, and the exhaust isolation valve 9 and the exhaust fan 7 are controlled accordingly. Further, a radiation monitor 20 is provided in the exhaust duct 8 to monitor radioactivity in the exhaust gas flowing through the exhaust duct 8.

Further, the block circuit 18 has a built-in timer, and after a certain period of time has elapsed, the block circuit 18 is released and the exhaust isolation valve 9 is closed.

In the regular ventilation system with the above configuration, when the accident signal 11 is issued, this signal is blocked by the blocking circuit, so that even after the accident signal is issued, the exhaust isolation valve 9 is kept open and the exhaust fan 7 continues to operate. . This makes it possible to prevent a drop in negative pressure inside the building during the time lag,
If necessary, the negative pressure can also be controlled to be increased.

Normally, the capacity of the exhaust fan 7 in the ventilation system is very large, so
The differential pressure setting device 19 detects the negative pressure inside the building, closes the exhaust isolation valve 9, and stops the exhaust fan 7 to prevent excessive negative pressure.

Further, if the radiation monitor 20 detects high radioactivity in the exhaust gas flowing through the duct 8, the exhaust isolation valve 9 is closed and the exhaust fan 7 is stopped. In addition, even when power is lost, the exhaust fan 7 continues to rotate for a considerable time due to its inertia and can maintain negative pressure inside the building, but since there is a time limit to its exhaust capacity, the timer built in the block circuit 18 After a certain period of time has elapsed, the block circuit is released and the exhaust isolation valve 9 is closed.

By doing as described above, the negative pressure inside the building can be controlled and maintained until the emergency gas processing equipment starts its rated operation after the accident signal is issued.

[Effects of the Invention] As is clear from the above, in the radioactive material release reduction equipment of the present invention, in the event of a nuclear reactor accident, from the time the accident signal is issued until the emergency gas processing system reaches the rated operating state,
Since the regular ventilation system controls and maintains the negative pressure inside the building, it is possible to prevent the direct dissipation of radioactivity from the building due to a drop in the negative pressure inside the building.

In addition, in the event of an accident, as mentioned above, the regular ventilation system operates to prevent the negative pressure inside the building from decreasing until the emergency gas treatment system reaches its rated operation, so radioactivity leaking into the reactor building is prevented. is emitted from the exhaust stack to a high place and does not become uncontrollably released to a low place, making it possible to control exposure.

[Brief explanation of drawings]

FIG. 1 is a system diagram of an embodiment of the present invention, and FIG. 2 is a system diagram of a conventional radioactive material release reduction facility. 1... Reactor building 2... Air supply system
3... Air supply fan 4... Air supply duct 5... Air supply isolation valve 6... Exhaust device
7... Exhaust fan 8... Exhaust duct 9... Exhaust isolation valve 10... Exhaust pipe 1l... Accident signal 12... ...Inlet valve
13...Flow rate adjustment valve 14...Drying device 15...Blower 16...Filter device 17...Outlet valve 18... ...Block circuit 19...Differential pressure setting device 20...
・Radiation monitor

Claims (1)

[Claims] The accident occurred in a system that has a regular ventilation system equipped with a supply air fan, an exhaust fan, a supply air isolation valve, and an exhaust isolation valve, and an emergency gas treatment system that removes radioactive materials and exhausts the building in the event of an accident. A radioactive material release reduction facility characterized in that the operation of the regular ventilation system is sometimes continued until the rated operation of the emergency gas treatment system is reached.